Brent crude oil futures LCOc1, the global benchmark used to trade oil, soared to its highest since July 6, 2015 to $55.20 a barrel. It last traded at $55.08 a barrel, up 62 cents, or 1.1 percent, at 0946 GMT. WTI crude oil CLc1 traded up 54 cents, or 1 percent, at $52.22 a barrel.

Front-month Brent crude futures LCOc1 were down 45 cents, or 0.8 percent by 0951 GMT (4:51 a.m. ET) from their last settlement at $53.49 per barrel. The contract was up more than 13 percent this week, its biggest gain since March 2009. U.S. West Texas Intermediate (WTI) futures CLc1 were at $50.68, down 38 cents.

Oil prices slipped on Friday as some investors opted to cash out after Brent touched 16-month a high on Thursday, with optimism over this week's OPEC-Russia accord on cutting output giving way to questions on the "sticking point" of implementing the deal.

U.S. crude oil CLc1 added to overnight gains of 9 percent to reach $50.00 a barrel for the first time since October. Brent crude LCOc1, which soared $4 overnight, touched a six-week peak of $52.73 a barrel.

Brent crude, the international oil marker, rose more than $3.00, or 7.2 per cent, to $49.73 in the late morning in London.

Brent crude futures LCOc1 fell as far as 2 percent before clawing back to trade up 29 cents at $47.44 per barrel at 1008 GMT. U.S. West Texas Intermediate (WTI) crude futures CLc1 also recouped early losses and were trading up 15 cents at $46.21 per barrel.

At 1040 GMT (5:40 a.m. ET), Brent crude futures LCOc1 were trading at $48.89, down 6 cents from their close. U.S. West Texas Intermediate (WTI) crude CLc1 was down 2 cents at $47.94 per barrel.

Brent crude oil futures LCOc1 were up 85 cents a barrel at $49.75 by 1000 GMT (5:00 a.m. ET), having earlier risen $1 in a push against the $50 mark for the first time since the end of October. U.S. West Texas Intermediate (WTI) crude futures CLc1 were up 68 cents, or 1.4 percent, at $48.92 a barrel.

Brent crude oil LCOc1 was up 60 cents a barrel at $47.23 by 1120 GMT (6:20 a.m. ET). U.S. light crude CLc1 was up 50 cents at $46.07.

Brent crude oil LCOc1 was up 60 cents a barrel at $47.23 by 1120 GMT (6:20 a.m. ET). U.S. light crude CLc1 was up 50 cents at $46.07.